This invention relates to automatic screw machines, and more particularly to an improved mechanism for chucking bar stock in such machines.
In screw machines of the type described a plurality of metal bars (bar stock) are chucked or otherwise releasably secured in rotating, collet-type chucking devices. During a machining operation the forward end of a piece of bar stock is engaged by one or more cutting tools, such as for example threading rolls or the like, after which the machined portion of the stock is cut off from its forward end. The associated chucking device or mechanism is then momentarily opened and the bar stock is fed forwardly again to bring another portion thereof into registry with the associated cutting or threading tools.
U.S. Pat. No. 4,014,558, which is owned by the same assignee as the present application, discloses an automatic screw machine having a chuck operating mechanism that utilizes a plurality of ball bearings, which are movably mounted in a plurality of arcuate pockets or recesses formed in one end of an annular ball cage, which is surrounded by a ball sleeve that is mounted for limited axial reciprocation. When the sleeve is in a retracted position it permits the balls to roll slightly radially outwardly to permit a spring to shift an outer, collet-operating spindle rearwardly to open the associated chucking mechanism. When the sleeve is advanced forwardly it urges the balls radially inwardly against an inclined cam surface which causes the balls to shift the outer spindle axially forwardly in a direction to close the chucking mechanism. In this type of device it is the radial and axial movement of the balls which transmit the opening and closing motion to the collet and chuck operating spindle.
Similar such mechanisms are disclosed in U.S. Pat. Nos. 3,741,572; 2,735,687; 3,176,553; and 4,418,925, except that the latter patent employs, instead of spherically shaped balls, arcuate, generally wedge shaped members, which are mounted for limited radial and axial movement in order to effect opening and closing of an associated collet or chucking mechanism.
The U.S. Pat. Nos. 2,728,579 and 4,171,820 also utilize spherically shaped balls for effecting the opening and closing of a collet or chucking mechanism, but differ from the above-noted prior art patents in that the balls are carried in circular openings in a pivotal operating arm for translational movement by the arm between opening and closing positions. The disadvantage of all of the above-noted prior art devices is that, although in many such mechanisms spherical balls are employed for effecting the opening and closing of a chucking mechanism, the balls are not mounted for simple rotation, but in each case are enclosed within sockets or circular recesses which are utilized to restrain the balls for limited rotational and translational movements. Moreover, in each such case the mechanisms which are employed to retain the balls are rather complicated and extremely expensive to manufacture, assemble, and replace.
It is an object of this invention, therefore, to provide an improved chucking mechanism which, although it utilizes spherical, steel balls for effecting the opening and closing of an associated chucking device, the overall mechanism is substantially more efficient and less complicated to manufacture and assemble.
Still another object of this invention is to provide an improved chuck operating mechanism of the type described which substantially reduces the overall number of parts which are necessary for effecting chucking operations.
Another object of this invention is to provide an improved chucking mechanism which does not require any particular adjustment to its various parts when its associated chucking collet is changed or repaired.
It is an object also of this invention to provide an improved, spring-loaded chucking mechanism which permits relatively simple adjustment of the tension in the associated spring means.
A particular object of this invention also is to provide an improved chucking mechanism which utilizes steel balls for effecting the opening and closing of the associated chucking device, but without utilizing the balls for imparting rotation to any portion of the mechanism.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings.